diff --git a/brain/validator/dataset.py b/brain/validator/dataset.py
index 67b378db0..c5c4d4ff1 100644
--- a/brain/validator/dataset.py
+++ b/brain/validator/dataset.py
@@ -43,6 +43,7 @@ def validate_classification(self, data):
             Required('independent-variables'): [{
                 Required(All(string_types[0], Length(min=1))): Coerce(float),
             }],
+            Required('error'): Any(None, string_types[0]),
         })
 
         for instance in data:
@@ -72,6 +73,7 @@ def validate_regression(self, data):
             Required('independent-variables'): [{
                 Required(All(string_types[0], Length(min=1))): Coerce(float),
             }],
+            Required('error'): Any(None, string_types[0]),
         })
 
         for instance in data: